4.2.12. PerlSetupEnv

Certain Perl modules used in CGI code (such as
CGI.pm) rely on a number of environment variables
that are normally set by mod_cgi. For example, many modules depend on
QUERY_STRING, SCRIPT_FILENAME,
and REQUEST_URI. When the
PerlSetupEnv directive is turned on,
mod_perl provides these environment variables in the same fashion
that mod_cgi does. This directive is On by
default, which means that all the environment variables you are
accustomed to being available under mod_cgi are also available under
mod_perl.

The process of setting these environment variables adds overhead for
each request, whether the variables are needed or not. If you
don't use modules that rely on this behavior, you
can turn it off in the general configuration and then turn it on in
sections that need it (such as legacy CGI scripts):